Antibodies to the class 2/3 OMPs are bactericidal and antigenic diversity between these proteins forms the basis of the current serotyping classification. The class 3 protein genes of several serotypes have been sequenced and areas of variability described which correspond to the surface exposed loops of the mature porin protein. These loops probably contribute to the serotype specific antigenic epitopes. We have examined the variable regions of 13 class 3 OMPs as they relate to serotype and have developed olionucleotide probes for identification and classification using genetic techniques.Complete class 3 gene sequences were obtained from prototype strains for serotypes 3, 14, 17, 18, 19, a Brazilian outbreak strain, BB1350 (serotype 4), and M978 (serotype 8). The porB gene sequences for strains of serotypes 1, 4, 12, 15, and 21 were obtained from GenBank. Multiple sequence alignment revealed four regions of major variability (VR1, VR2, VR3, and VR4) corresponding to leeps I, V, VI and VII of the folded protein. Analysis of individual variable region bucleic acid sequences revealed a pattern consistent with horizontal genetic exchange. The 11 serotype sequences examined showed between 4 and 7 different sequence patterns.Biotin labeled oligonucleotide probes to all major variable region sequences were synthesized. Probes identifying serotypes 4, 12, 15, 17, and 21 have been tested using dot-blot hybridization assays of genomic DNA from each prototype serotype strain and multiple clinical isolates. A subgroup of serotype 4 strains was demonstrated. Additionally, a series of non- serotypeable strains were tested and approximately half were found to have one or more VR sequences in common with known serotype strains.To further examine the relationship between VR sequence and antigenicity, we are attempting to express the N. meningitidis porin protein on the surface of an E. coli expression vector.